This invention relates to a damper control arrangement and in particular relates to a damper control arrangement including means to selectively control the opening area of a flow through orifice. Even more particularly, this invention relates to a damper control arrangement which provides a selectively buffered transition in a system when starting or stopping the flow of fluid in the system.
In many applications it is desirable to provide for a buffered transition when removing a fluid system from or returning a fluid system to different preselected fluid flow conditions. For example, in the filtering of a gas stream using cloth fabric bags, it is desirable to avoid a sudden surge of gas when a gas controlling damper arrangement is activated, the sudden surges of gas causing the fabric filter bags to snap and consequently weaken the fabric material. This weakening of the fabric is intensified when the fabric material is one containing glass fibers.
Prior art damper arrangements, such as bullseye dampers and butterfly dampers, can only be made to function satisfactorily by using an expensive time actuating means which causes them to operate in a relatively slow manner. Even so, butterfly dampers are particularly difficult to use because the fluid flow rate does not change linearly with respect to the change in position of the damper blade as most of the fluid is controllable when the damper blade moves to a position substantially parallel to the direction of flow of the fluid. Less objectionable is the bullseye damper since its flow rate changes linearly over the entire damper blade stroke.
In order to provide a control arrangement for a damper to selectively control the opening and closing of a flow-through orifice to provide a selectively buffered transition in a system when starting or stopping the flow of fluid therethrough, U.S. Pat. No. 3,898,997 has been proposed utilizing electrical actuating means to actuate the damper means for movement of the damper blade from one position to another. In this reference, when the damper blade is in an open position, a solenoid is required to be energized. Furthermore, when the device taught by the reference is used in combination with a filter system utilizing a baghouse and the damper assembly is disposed in a inlet air system to the baghouse, when a compartment is being cleaned the damper is closed and one solenoid is de-energized, but a second solenoid is required to be energized. When putting the system back onstream and a soft-inflate is required, the one solenoid is energized and the second solenoid is de-energized until a preselected distance or preselected period of time has been satisfied. Then, the energized solenoid is de-energized. After the cycle is ready to end the low flow rate, the de-energized solenoid is then re-energized to open the damper and remains in the energized position during the normal operation of the system.